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From Bertrand Dechoux <decho...@gmail.com>
Subject Re: dfs.name.dir replication and disk not available
Date Fri, 28 Sep 2012 12:54:07 GMT
That's definitely clearer (and it makes sense).

Thanks a lot.

Bertrand

On Fri, Sep 28, 2012 at 11:56 AM, Harsh J <harsh@cloudera.com> wrote:

> I don't know how much of this is 1.x compatible:
>
> - When a transaction is logged and sync'd, and a single edits storage
> location fails during write, then only that storage location is
> ejected out of the regular write list and skipped over (with states
> being updated for that location in the UI, etc., immediately). The
> rest remain active and NN lives on. The transaction is marked
> successful and returns back to client with a similar code. Further
> transactions too skip the ejected storage.
> - If no edit streams remain after removal (i.e. last remaining disk is
> removed due to a write error), then the transaction is failed and the
> NN dies down, to prevent data loss due to lack of persistence.
> - Hence, a transaction at the NN can be marked complete and return a
> success, iff, at least one location successfully wrote the edit log
> for it.
> - If dfs.name.dir.restore is enabled, then the NN checks if its
> ejected storages are healthy again and re adds them. The check, IIRC,
> is done during checkpoint or checkpoint-like operations currently.
>
> I guess all of this is in 1.x too, but I haven't validated it
> recently. It is certainly in the versions I've been using and
> supporting at my org for quite a while now. The restore especially
> comes in handy for customers/users with fairly common NFS mount
> related issues, not requiring them to restart NN each time the NN
> ejects the NFS out for a bad write. Although, for that to happen, a
> soft mount is necessary and recommended, rather than a hard mount,
> which would hang the NameNode and invalidate its whole "still
> available despite a few volumes failing" feature.
>
> Does this help Bertrand? Happy to answer any further questions.
>
> On Fri, Sep 28, 2012 at 2:51 PM, Bertrand Dechoux <dechouxb@gmail.com>
> wrote:
> > Hi,
> >
> > I was wondering about the safety of multiples dfs.name.dir directories.
> > On one hand, we want all copies to be synchronised but on the other hand
> if
> > a hard drive fail we would like the namenode still to be operational.
> > How does that work? I know there is the source but I was hoping for a
> higher
> > level description.
> >
> > Regards
> >
> > Bertrand
> >
> > PS : I am interested about the behaviour of the last stable version ie
> > 1.0.3. Not in the old issues that were solved.
>
>
>
> --
> Harsh J
>



-- 
Bertrand Dechoux

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